Multi-chip module with stacked dice

ABSTRACT

A multi-chip module may be formed by wire bonding a first chip within a cavity in a multi-chip carrier. A second die may be positioned over the first die, elevated therefrom, using bump bonding. In some embodiments, only a single cavity is utilized and in other embodiments, multiple cavities may be utilized, one of which mounts a first chip and the other of which mounts a second chip. In some embodiments, the second chip may be a composite of two dice coupled back-to-back so that the lowermost die may be bump bonded to the carrier and the uppermost die, facing upwardly away from the carrier, may be wire bonded thereto.

This is a divisional of prior application Ser. No. 09/437,595 filed Nov.10, 1999, now U.S. Pat. No. 6,207,467.

BACKGROUND

This invention relates generally to packaging integrated circuit dice inmulti-chip modules.

In a variety of applications it is desirable to package more than onedie in a single integrated circuit package. This may be the result oflimits on the integratability of the components on the two dice into asingle semiconductor die. These limitations may arise from the limits onthe ability to integrate components into a single package. They may alsoarise from the fact that the components on the packages are incompatiblewith one another. For example, components on the two different dice maybe subject to different voltage requirements. Alternatively, the twodice may require processing techniques which are incompatible.

In a number of cases, it may be desirable to package two dice into onepackage and to couple both dice through a common set of contacts to theoutside world. Generally a die has a top side which contains contactsfor making an electrical connection to the outside world and a bottom orbackside. A challenge that arises is to put together a plurality of diceinto a single package when each die can be only contacted on one side.

Thus, there is a continuing need for better ways to package multipledice in a single package.

SUMMARY

In accordance with one aspect, a method of making multi-chip modulesincludes wire bonding a first die to contact in a first cavity of astructure. A second die is bump bonded through a contact on thestructure over the first die. A solder ball is attached to the structureso that the solder ball is electrically coupled to the first and seconddice.

Other aspects are set forth in the accompanying detailed description andclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a process flow for one embodiment of the present invention;

FIG. 2 is an enlarged cross-sectional view through one embodiment of thepresent invention;

FIG. 3 is an enlarged cross-sectional view through another embodiment ofthe present invention;

FIG. 4 is an enlarged cross-sectional view through still anotherembodiment of the present invention;

FIG. 5 is an enlarged cross-sectional view through yet anotherembodiment of the present invention; and

FIG. 6 is an enlarged cross-sectional view through another embodiment ofthe present invention.

DETAILED DESCRIPTION

A process for attaching more than one die to a carrier for making amulti-chip module is illustrated in FIG. 1. Initially, a peripheral bondchip is attached to a multi-cavity structure, as indicated at block 100.A peripheral bond chip includes a plurality of bond pads around itsperipheral edges which are available for wire bonding. A multi-cavitystructure is a chip carrier which includes more than one receiving areafor integrated circuit dice or chips. In some cases, the multi-cavitystructure includes die-receiving cavities which are vertically spacedwith respect to one another. The die may be stacked one on top of theother with spacing between the dice.

After the peripheral bond chip has been attached by wire bonding, theresulting structure is tested in strip form for device functionality(block 102). Bad units are marked for subsequent flow identification andelimination from the assembly flow. In this way, the module may betested prior to putting two dice into the module. This saves the cost ofrecovering the second die where either the module or the first inserteddie is bad.

After the functionality test, the next step is to attach a bumped chipover the peripheral bond chip (block 104). The bumped chip is one whichhas solder bumps or solder balls which may be heat softened forattachment to other electrical devices.

After attaching the bumped chip, usually in a stacked arrangement overthe peripheral bond chip, the entire assembly may be overmolded andcured (block 106). Thereafter solder balls are used to attach the moduleto peripheral components such as a printed circuit board, as indicatedin block 108.

Referring now to FIG. 2, a multi-chip module 10, made by the processillustrated in FIG. 1, includes a multi-cavity structure 12, a pluralityof externally attached solder balls 14 and an overmolding 16. In thiscase, the structure 12 includes a set of three cavities including alowermost cavity 26, a vertically upwardly displaced cavity 28 and anuppermost cavity 30. Thus, the cavities 26, 28 and 30 which becomeprogressively larger from bottom to top, define a plurality of steps inthe sidewalls of the structure 12.

A peripheral bond chip 18 is attached to the lowermost cavity 16 by wirebonding peripheral wire bond pads 17 on the chip to corresponding wirebond pads 33 on the second cavity 28. At this point, the entire assemblyis tested.

Next, a bumped chip 22 is secured to the uppermost cavity 30 using bumpbonding by way of solder balls or bumps 24. Thereafter, the entireassembly is overmolded so that the overmolding 16 actually covers aportion of the upper surface 32 of the structure 12.

The connections between the external solder balls 14 and the die 22 and18 may be accomplished in a variety of ways. Where the structure 12 is alaminate, conductive traces 34 may extend through the structure 12 in agenerally horizontal configuration. The traces 34 may be electricallyisolated by intervening insulating layers. Vertical connections may bemade to overlying contact pads on the cavities 28 and 30 by way of vias36. Contacts may then be made downwardly to bond pads 39 coupled to thesolder balls 14 by way of vias 38. Of course, other techniques may beutilized as well.

Thereafter, the package 10 may be surface mounted on a suitable devicesuch as a printed circuit board (not shown). This is accomplished bysimply positioning the module 10 on the board and heat reflowing tocause the solder balls 14 to physically and electrically couple themodule 10 to the underlying device.

The lower die 18 may be physically connected to the structure 12 by wayof a suitable die attach. A suitable die attach includes conductivepaste, an adhesive tape, or adhesive such as an epoxy.

Referring next to FIG. 3, a multi-chip module 10A includes a structure12A. A die 18 is coupled to a cavity 42 using wire bond wires 20 asdescribed previously in connection with the module 10 and the cavity 26.In this case, a die 22 is bump bonded to the upper surface 40 of thestructure 12A. Again, bumps 24 are utilized to bump bond the die 22 tocontacts in the upper surface 40 of the structure 12A. The connectionsfrom the bumps 24 and wire bonds 20 to the solder balls 14 may be madeusing any conventional technique, including the laminate techniqueillustrated in FIG. 2.

In effect, the overmolding 16 extends upwardly to accommodate the upperdie 22. Overall, a lower profile may be attained. This is accomplishedby eliminating in effect the second cavity and coupling the wires 20 andthe bumps 24 to the same surface 40. This is generally not a problembecause the wire bonding is done first before the upper die 22 ispositioned. Then, the bumps 24 are made sufficiently large to provideadequate spacing over the wire bond wires 20.

Turning next to FIG. 4, a multi-chip module 10B which receives threedice includes a structure 12A having an upper surface 40 as describedpreviously in connection with FIG. 3. in addition, the structure 12A iselectrically coupled (as described previously) to solder balls 14. Inthis case, a pair of dice 44 and 46 are secured to the cavity 42. Thedice 44, 46 are wire bonded by way of wires 48 to contacts on the uppersurface 40 and are bonded together by intervening wire bond wire 50.Thus, wire bonding may be completed while the dice 44 and 46 areexposed. The dice 44 and 46 may actually extend upwardly above the uppersurface 40 of the cavity 42.

Thereafter, the die 22 is attached to the upper surface 40 as describedpreviously. The entire assembly is overmolded again as described inconnection with the embodiment of FIG. 3.

Another multi-chip module 10C which can contain multiple die, shown inFIG. 5, includes a structure 12 as previously illustrated in connectionwith FIG. 2. The attachment of each die 18, 68 is generally as describedabove in connection with FIG. 2 except that a composite die 68 may beattached to the uppermost cavity 30. The composite die 68 may be made upof a pair of dice 66, 70 attached back-to-back so that their top sides69 extend in opposite directions. A lower die 66 may extend beyond theupper die 70. The two die 66, 70 may be connected to one another usingadhesive techniques, tape techniques, or conductive paste as examples.

The lower die 66 may be secured to the uppermost cavity 30 using bumpbonding by way of bumps 24. The upper die 70 is then wire bonded, usingperipheral wire bond contacts and bond wires 64 to the upper surface 32of the structure 12. As before, the entire assembly is overmolded asindicated at 16. Electrical connections may be made through thestructure 12 in any of a variety of ways, including the techniqueillustrated in FIG. 2.

Although an offset 56 is created between the two dice 66 and 70, this isnot essential. The wire bonding can proceed in the same way even if thetwo dice have substantially the same dimensions.

Turning finally to FIG. 6, a module 10D with three dice includes astructure 12A of the type previously described in connection with FIG.3. Again, solder balls 14 are provided on the lower external surface ofthe structure 12A. As before, a die 18 is secured in the cavity 26 usingperipheral wire bond wire 20.

A composite die 68 is formed as described previously in connection withFIG. 5. A lower die 66 is bump bonded using bumps 24 to the uppersurface 40 of the structure 12A. The upper die 68 is wire bonded, usingwire bonds 64, to the upper surface 40. By extending the wire bonds 64outwardly with respect to the bumps 24, both dice 66, 70 may be coupledto the same surface.

Separation or isolation of the signals may be possible by having viaswhich extend through the structure 12A to different depths. For example,as shown in FIG. 6, each of the wire bond wires 64 and bumps 24 may becoupled by a contact 72 through a via 73 to a trace 74, 76. The traces74 and 76 may be formed at the same level within the carrier 12A but maybe separated by an insulating gap. The gap may be defined during thephotolithographic techniques used to form the trace layer. Vias 78 and80 then extend downwardly to isolated traces 82 and 84. The traces 82and 84 then contact by way of vias 86 and 88 to pads 90 which in turnare coupled to solder balls 14. While one technique has been describedfor coupling the signals independently to the solder balls 14, thoseskilled in the art will appreciate a number of other techniques fordoing the same thing.

While the present invention has been described with respect to a limitednumber of embodiments, those skilled in the art will appreciate numerousmodifications and variations therefrom. It is intended that the appendedclaims cover all such modifications and variations as fall within thetrue spirit and scope of this present invention.

What is claimed is:
 1. A multi-chip module comprising: a structure having a cavity for receiving a die; a first die having a top side and a backside, said backside mounted in said cavity and said top side wirebonded to said structure; a second die mounted in said structure over said first die, said second die being bump bonded to said structure; and solder balls secured on said structure, said solder balls electrically coupled to said first and second dice.
 2. The module of claim 1 wherein said structure is a multi-cavity structure including three cavities of progressively larger size as they extend upwardly through said structure.
 3. The module of claim 2 wherein said first die is mounted in a first cavity and is wire bonded to said second cavity, said second die being bump bonded to said third cavity.
 4. The module of claim 1 wherein said structure includes a single cavity and an upper surface.
 5. The module of claim 4 wherein said first die is mounted in said cavity and is wire bonded to said upper surface, said second die being bump bonded to said upper surface at a point spaced outwardly from the location at which said first die is wire bonded to said upper surface.
 6. The module of claim 5 including a third die mounted in said cavity alongside said first die, said first die being wire bonded to said upper surface and to said third die and said third die being wire bonded to said first die and said upper surface.
 7. The module of claim 5 wherein said second die is formed of two dice secured in back-to-back relationship, the uppermost die of said composite second die being wire bonded to said upper surface and the lowermost die of said composite die being bump bonded to said upper surface, said first die being bonded to said upper surface, said lowermost die being bump bonded to said upper surface at a point spaced from the point where said first die is bonded to said upper surface.
 8. The module of claim 1 wherein said second die is a composite die having contacts on two outwardly facing sides of said composite die, one of said outwardly facing sides being wire bonded to said structure and the other of said outwardly facing sides being bump bonded to said structure.
 9. The module of claim 8 wherein said structure includes at least two cavities, said composite die having one side bump bonded to the uppermost of said cavities and the other side being wire bonded to said structure.
 10. The module of 9 including a first cavity mounting said first die and a second cavity, said first die being wire bonded to said second cavity, said structure including an upper surface and a third cavity, said second die bump bonded to a third cavity and wire bonded to the upper surface of said structure.
 11. A multi-chip module comprising: a carrier having a first side and a second side and a cavity formed in said first side; first and second chips mounted on said first side of said carrier with said second chip over said first chip, said first chip secured to said carrier in said cavity; said first and second chips being electrically coupled to said first side, said second chip being bump bonded to said first side and said first chip being wire bonded to said first side.
 12. The module of claim 11 wherein said second chip is electrically coupled to said first side outwardly with respect to the location where said first chip is coupled to the said first side.
 13. The module of claim 12 including a third chip contained in said cavity with said first chip.
 14. The module of claim 11 wherein said second chip is made up of a pair of dice coupled together in back to back relationship.
 15. The module of claim 14 wherein one of said dice is bump bonded to said first side and the other of said dice is wire bonded to said first side.
 16. A multi-chip module comprising: a carrier including a cavity; a first chip secured to said carrier in said cavity; and a second chip including a pair of dice secured to one another in back to back relationship, said second chip secured to said carrier over said first chip.
 17. The module of claim 16 wherein said second chip is secured to a second cavity defined in said module.
 18. The module of claim 16 wherein said second chip is secured on an upper surface of said carrier.
 19. The module of claim 16 wherein one of said dice is wire bonded to said carrier and the other of said dice is bump bonded to said carrier.
 20. The module of claim 19 wherein said dice are bonded to different surfaces of said carrier. 